1. Field of the Invention
The present invention relates to laminated ceramic electronic devices, and more particularly, to a laminated ceramic capacitor having a superior resistance to the expansion and contraction of a circuit board and having superior resistance to bending thereof.
2. Description of the Related Art
A typical laminated ceramic capacitor is composed of a ceramic laminate having internal electrodes therein, and external electrodes. The ceramic laminate is formed by baking a green ceramic laminate composed of a plurality of green ceramic layers, which are formed of a dielectric material, and internal electrodes provided between the ceramic layers. The internal electrodes are formed by steps of printing a conductive paste on a plurality of green ceramic layers and baking the conductive paste printed on the plurality of green ceramic layers constituting the green ceramic laminate. Each internal electrode is formed so that an end thereof is exposed at one of edge surfaces of the ceramic layer. The external electrodes are formed by the step of coating a conductive paste on edge surfaces of the ceramic laminate so as to be connected to the ends of the internal electrodes exposed at the edge surfaces of the ceramic laminate, and the step of baking the conductive paste.
The conductive paste for forming external electrodes is primarily composed of a conductive component, an inorganic binder and an organic vehicle. In particular, in the case in which a base metal, such as copper (Cu) or nickel (Ni), is used as the conductive component, baking is performed in a nitrogen (N2) atmosphere in order to prevent the conductive component from being oxidized. As an inorganic binder used when baking is performed in a N2 atmosphere, a barium oxide (BaO)-based glass is disclosed in Japanese Examined Utility Model Application Publication No. 58-14600, and a zinc oxide (ZnO)-based glass is disclosed in Japanese Examined Patent Application Publication No. 4-15606.
A conductive paste using the glass mentioned above as an inorganic binder can be baked in a N2 atmosphere; however, the adhesive strength of the conductive paste to a ceramic body is low. Accordingly, in the case in which a laminated ceramic capacitor having external electrodes formed of the conductive paste described above, is mounted on a circuit board, when the ambient temperature abruptly changes or when a thermal shock is applied to the laminated ceramic capacitor, cracking may occur inside the laminated ceramic capacitor in some cases due to the stress generated by expansion and contraction of the circuit board and/or the stress generated by bending of the circuit board caused by an external force. In recent years, concomitant with the trend toward thinner capacitors approximately 0.3 to 2.0 mm thick, the thicknesses of ceramic layers have decreased to approximately several to 30 mm, and the thicknesses of internal electrodes have decreased to approximately 0.5 to 2.0 xcexcm. For the laminated ceramic capacitor described above, the occurrence of internal cracks will result in catastrophic failure.
In consideration of the problem described above, an object of the present invention is to provide a laminated ceramic electronic device having a superior resistance to the expansion and contraction of a circuit board and having superior resistance to bending thereof. In particular, the laminated ceramic electronic device of the present invention has a mechanical strength withstanding the stress generated by expansion and contraction of the circuit board caused by a thermal shock when mounting is performed thereon and withstanding the stress generated by bending of the circuit board caused by an external force applied thereto.
To this end, the laminated ceramic electronic device of the present invention comprises a plurality of ceramic layers, a plurality of internal electrodes formed between the ceramic layers, and external electrodes connected to the internal electrodes, wherein the external electrode contains a conductive component and an inorganic binder having a Young""s modulus of about 9.0xc3x97109 Pa or less.